KI + Pb = K + PbI2

KI potassium iodide + Pb lead ⟶ K potassium + PbI_2 lead iodide

Balance the chemical equation algebraically: KI + Pb ⟶ K + PbI_2 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 KI + c_2 Pb ⟶ c_3 K + c_4 PbI_2 Set the number of atoms in the reactants equal to the number of atoms in the products for I, K and Pb: I: | c_1 = 2 c_4 K: | c_1 = c_3 Pb: | c_2 = c_4 Since the coefficients are relative quantities and underdetermined, choose a coefficient to set arbitrarily. To keep the coefficients small, the arbitrary value is ordinarily one. For instance, set c_2 = 1 and solve the system of equations for the remaining coefficients: c_1 = 2 c_2 = 1 c_3 = 2 c_4 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 2 KI + Pb ⟶ 2 K + PbI_2

+ ⟶ +

potassium iodide + lead ⟶ potassium + lead iodide

Construct the equilibrium constant, K, expression for: KI + Pb ⟶ K + PbI_2 Plan: • Balance the chemical equation. • Determine the stoichiometric numbers. • Assemble the activity expression for each chemical species. • Use the activity expressions to build the equilibrium constant expression. Write the balanced chemical equation: 2 KI + Pb ⟶ 2 K + PbI_2 Assign stoichiometric numbers, ν_i, using the stoichiometric coefficients, c_i, from the balanced chemical equation in the following manner: ν_i = -c_i for reactants and ν_i = c_i for products: chemical species | c_i | ν_i KI | 2 | -2 Pb | 1 | -1 K | 2 | 2 PbI_2 | 1 | 1 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression KI | 2 | -2 | ([KI])^(-2) Pb | 1 | -1 | ([Pb])^(-1) K | 2 | 2 | ([K])^2 PbI_2 | 1 | 1 | [PbI2] The equilibrium constant symbol in the concentration basis is: K_c Mulitply the activity expressions to arrive at the K_c expression: Answer: | | K_c = ([KI])^(-2) ([Pb])^(-1) ([K])^2 [PbI2] = (([K])^2 [PbI2])/(([KI])^2 [Pb])

Construct the rate of reaction expression for: KI + Pb ⟶ K + PbI_2 Plan: • Balance the chemical equation. • Determine the stoichiometric numbers. • Assemble the rate term for each chemical species. • Write the rate of reaction expression. Write the balanced chemical equation: 2 KI + Pb ⟶ 2 K + PbI_2 Assign stoichiometric numbers, ν_i, using the stoichiometric coefficients, c_i, from the balanced chemical equation in the following manner: ν_i = -c_i for reactants and ν_i = c_i for products: chemical species | c_i | ν_i KI | 2 | -2 Pb | 1 | -1 K | 2 | 2 PbI_2 | 1 | 1 The rate term for each chemical species, B_i, is 1/ν_i(Δ[B_i])/(Δt) where [B_i] is the amount concentration and t is time: chemical species | c_i | ν_i | rate term KI | 2 | -2 | -1/2 (Δ[KI])/(Δt) Pb | 1 | -1 | -(Δ[Pb])/(Δt) K | 2 | 2 | 1/2 (Δ[K])/(Δt) PbI_2 | 1 | 1 | (Δ[PbI2])/(Δt) (for infinitesimal rate of change, replace Δ with d) Set the rate terms equal to each other to arrive at the rate expression: Answer: | | rate = -1/2 (Δ[KI])/(Δt) = -(Δ[Pb])/(Δt) = 1/2 (Δ[K])/(Δt) = (Δ[PbI2])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| potassium iodide | lead | potassium | lead iodide formula | KI | Pb | K | PbI_2 Hill formula | IK | Pb | K | I_2Pb name | potassium iodide | lead | potassium | lead iodide

| potassium iodide | lead | potassium | lead iodide molar mass | 166.0028 g/mol | 207.2 g/mol | 39.0983 g/mol | 461 g/mol phase | solid (at STP) | solid (at STP) | solid (at STP) | solid (at STP) melting point | 681 °C | 327.4 °C | 64 °C | 402 °C boiling point | 1330 °C | 1740 °C | 760 °C | 954 °C density | 3.123 g/cm^3 | 11.34 g/cm^3 | 0.86 g/cm^3 | 6.16 g/cm^3 solubility in water | | insoluble | reacts | dynamic viscosity | 0.0010227 Pa s (at 732.9 °C) | 0.00183 Pa s (at 38 °C) | |